Process for the production of alloys of the alkaline earth metals with cadmium



Patented Feb. 18, 1936 UNITED STATES PATENT OFFICE.

mocEss FOR THE PRODUCTION or AL- LOYS or THE ALKALINE EARTH METALS wrrn CADMIUM Gustaf Newton Kirsebom, Oslo, Norway, assignor to Calloy Limited, London, England, an English joint-stockcompany June 11, 1932 11 Claims.

This invention relates to a new or improved method or process for the production of alkaline earth metals and alloys thereof with cadmium such as are hereinafter defined and as disclosed in my copending. application Serial No. 648,443 filed December 22, 1932, of which this application is a division. I

There are certain metals, especially cadmium, which do not readily alloy with aluminium when both are in a molten condition and in the presence of each other, e. g. when molten cadmium is added to a bathof molten aluminium (or when cadmium and aluminium aremelted together) these two metals will not form an alloy but will form separate layers which are not substantially soluble in each other; and this I utilize in the process according to the, present invention for the production of alloys of the alkaline earth metals with cadmium.

. In my copending application for U. S. Patent Serial No. 620,574 filed July '2, 1932 (U. S. Patent No. 1,935,245) .I have described a process for producing alloys ofthe. alkaline earth metals with aluminium (e. g. calcium-aluminium alloy, strontium-aluminium alloy, etc.) by the reduction of compounds of alkaline earth metals'by aluminium and the production thereby of said alloys of aluminium; such process being carried out by introducing one or more compounds of the alkallne earth metals in pieces not less than about 1 mm. size into a. bath of molten. aluminium thereby to reduce said compound or compounds and alloy said alkaline earth metal or metals with the aluminium.

Now the present invention is as follows:-

I have found that alloys of the alkaline earth metals with cadmium can be produced, readily and economically by reducing a compound of an alkaline earth metal in a bath of molten alu- (e. g. in the manner hereinbefore referred to) and, either before, during, or after, introducing said compound of the alkaline earth metals into said bath of molten aluminium, ad: mixing or otherwise bringing cadmium in a molten condition into contact with the molten aluminium alloy whereupon the alkaline earth metal leaves the aluminium and goes to the cadmium and alloys with the cadmium as aforesaid.

It is to be understood that the alkaline earth metals can be preparedby the process of the present inventionnot only from the alkaline earth metal oxides but also from other compounds of the alkaline earth metals, for example from the alkaline earth metal silicates.

-In the process as set out above it must be understood that the term alkaline earth metals" includes not only calcium, strontium and barium, but also magnesium and beryllium.

When the alloy of cadmium with the alkaline earth metal has been formedon completion of the alloying process-the cadmium can be distilled ofi so that the process affords a ready means ofpreparing the alkaline earth metals in substantially pure condition.

Broadly stated therefore the present invention is for a. process for preparing the alkaline earth metals and alloys thereof, which process comprises the steps of mixing together in the molten condition cadmium (which does not readily form an alloy with aluminium) and. an alloy with aluminium of the said alkaline earth metal ormetals and allowing the melt to form into two layers and separating the aluminium According to a further feature of my present invention the alkaline earth metals can be separated from the cadmium which does not readily alloy with aluminium as aforesaid; and this separation can be effected by the step of volatilizing off the volatile metal i. e. cadmium from the alloy containing it whereby the alkaline earth metal remains alone; and pure alkaline earth metal can thus be obtained.

The invention will now be more specifically described with the aid of examples.

(a) The aluminium alone may first be placed in the heating chamber and melted; and after the alkaline earth metal oxides in pieces or lumps have been placed on the bath of molten aluminium and reduced and an alloy of alkaline earth metal or metals and aluminium has thereby been formed as aforesaid; thereupon cadmium in a molten condition (or otherwise) is introduced into said bath of molten aluminium alloy through which latter the cadmium will descend and settle below same in the heating chamber; or

(b) The cadmium and aluminium may be heated (melted) together in a suitable heating chamber or the cadmium may be heated (melted) first and then the aluminium; and thereafter the alkaline earth metal oxides in other than powder form, 1. e. in pieces or lumps, introduced by placing said pieces or lumps on top of the molten aluminium.

Whereupon, whichever procedure is followed, it will be found that the alkaline earth metal or metals in the aluminium will have left the latter and gone into the cadmium and in alloy therewith.

(c) Or an alkaline earth metal alloy of aluminium may be melted down and molten cadmium added to the melt and thereupon the cadmium will extract the alkaline earth metal from the aluminium thus forming an alkaline earth metal alloy with the cadmium, which latter will sink to the bottom leaving the aluminium on top of the bath substantially free from alkaline earth metal.

For example, I have in this way melted down a calcium aluminium alloy containing 10% calcium, I have melted same at about 700 C. and, after having melted some cadmium at about 350 C. I have added this molten cadmium to the alloy bath; and on pouring out this melt I found that after cooling, there were present two different layers the top one consisting of substantially pure aluminium and the bottom layer of cadmium containing 6.5% Ca and containing but small traces of aluminium.

In a similar manner I have made strontium cadmium from strontium-aluminium alloy by pouring molten cadmium over the molten strontium-aluminium alloy, and in this way obtained a strontium cadmium of a crystalline structure and analyzing 5.3% strontium.

In a similar way I have produced barium cadmium containing 3% barium.

Similarly magnesium was introduced into cadmm from a magnesium-aluminium alloy containing up to 5% Mg.; and a magnesium cadmium alloy obtained running up to 2% Mg.

Also beryllium has been obtained in the cadmium in this way.

In the case of beryllium; the following is an example of carrying my present invention into practicez- To a molten bath of aluminium heated to about 1100 C. I add thereto natural beryl (in lumps or pieces) which is a mineral consisting of a beryllium aluminium silicate with a formula 3BeO.Al203.6SiO2.

By adding gradually the beryl in pieces to the metal (molten aluminium) this latter I found gradually rose in silicon content and I ended up with a metal containing 20% silicon, having thus reduced the silica in the beryl to silicon which alloyed with the aluminium. Although I have so far been unable to analyze this alloy for beryllium (the analysis of this metal with the presence of aluminium being extremely difficult) I have found that the alloy had a steel grey appearance suggesting the presence of beryllium. By then treating this alloy (beryllium-aluminium-silicon) with cadmium in the aforesaid manner, an alloy of cadmium and beryllium was formed (the cadmium becoming quite brittlewhich suggested that the beryllium had gone into the cadmium) and thereafter the cadmium can be distilled off thus leaving metallic beryllium.

I have found that the migration of the alkaline earth metal or metals into the cadmium takes place with great rapidity; e. g. only a few minutes after adding the cadmium the melt could be poured.

I have also found that if pure aluminium is melted down and alkaline earth metal oxide in l'ump form (1. e. in pieces and not in powder) is cadmiui'n then poured into this molten alloy,

the complete process can thus be carried out in one operation. 1

I have carried out this operation in a graphite crucible which was heated in a furnace of usual type to the desired temperatures.

Any suitable type of furnace can be used for the operation.

I have found that a great recovery of the alkaline earth metal or metals was obtained in the cadmium, in the case of extracting calcium from calcium-aluminium alloy by means of cadmium, viz. as much as of the calcium went into the cadmium, 'while not a trace of calcium was found in the remaining aluminium.

I have further found that it is possible to get higher percentages of the alkaline earth metal into the cadmium by passing the total amount of the cadmium to be passed once (or more than once if desired) through the bath of molten aluminium alloy slowly and well distributed throughout the bath in order to obtain a better contact of the alkaline earth metals.

A convenient way of securing good distribution of the cadmium throughout the bath is to add the cadmium in granulated form to the molten bath.

Furthermore (as aforesaid) the production of the aluminium alloy is not confined to oxides of the alkaline earth metals as starting materials, but other compounds may be used and in particular silicates. Thus if burnt magnesite rich in silica (16 per cent) is used, an aluminiummagnesium-silicon alloy is produced. In the same way other alkaline earth silicates produce the triple alloy of aluminium silicon and alkaline earth metal. When this triple alloy is treated with cadmium the alkaline earth silicide in the alloy is broken up, the alkaline earth metal going to the cadmium and the silicon remaining with the aluminium.

In the employment of cadmium as aforesaid the temperature of the aluminium alloy bath may advantageously be, for'example, 700-800 C. and then the cadmium in a molten condition is poured gradually into this bath.

The process of the invention may be carried out with more than one alkaline earth metal in the alloy with aluminium.

The amount or proportion of cadmium etc. to be added to the molten bath of aluminium alloy will depend on the results it is desired to obtain.

For example with equal proportions by weight of the aluminium and cadmium the percentage of the calcium in the aluminium (before transfer) will be about the same in the cadmium (after transfer); while with a smaller percentage of cadmium there will be a higher percentage of the calcium etc. in the cadmium.

What I claim is:

1. A process for preparing alkaline earth metal alloys for the production of cadmium alkaline earth metal alloys, which process comprises the step of mixing together in the molten condition cadmium and an alloy with aluminium containing the said alkaline earth metal and allowing the melt to form into two layers and separating the aluminium layer.

2. A process for preparing calcium alloys which process comprises the steps of mixing together in the molten condition metallic cadmium and an aluminium alloy containing calcium and allowing the melt to form into two layers and separating the aluminium layer.

3. A process for preparing metallic calcium, which process comprises the steps of mixing together in the molten condition metallic cadmium and aluminium alloy containing calcium, allowing the melt to form into two layers; separating the aluminium layer (mm the cadmium alloy and volatilizing cadmium from the latter whereby substantially pure calcium remains.

4. A process for preparing alkaline earth metals, which process comprises melting together an alkaline earth metal oxide in pieces more than 1 mm. in size and metallic aluminium and mixing therewith while in the molten condition metallic cadmium; allowing the melt to form into two layers; separating the aluminium layer and volatilizing oil the cadmium from the alloy containing it.

5. A process for preparing magnesium alloys, which process comprises the steps of mixing together in the molten condition metallic cadmium and an aluminium alloy containing magnesium; allowing the melt to form into two layers and separating the aluminium layer.

6. A process for preparing metallic magnesium, which process comprises the steps of mixing together in the molten condition metallic cadmium and an aluminium alloy containing magnesium; allowing the melt to form into two layers; separating the aluminium layer from the cadmium alloy and volatilizing cadmium from the latter, whereby substantially pure magnesium remains.

7; A process for preparing alkaline earth metals, which process comprises melting together ingredients which form an alloy containing the said alkaline earth metal and aluminium; mixing therewith while in the molten condition metallic cadmium; allowing the melt to form into which comprises in combination the steps of melting together calcium oxide in pieces of more than 1 mm. in size and metallic aluminium;

,mixing therewith, while in. the molten condition,

metallic cadmium; allowing the melt to form into two layers; separating the aluminium layer and volatilizing oil the cadmium from the alloy containing it.

9. A process for preparing metallic magnesium, which comprises in combination the steps of melting together magnesite in pieces more than 1 mm. in size and metallic aluminium; mixing therewith, while in the molten condition, metallic cadmium; allowing the melt to form into two layers; separating the aluminium layer and volatilizing off the cadmium from the alloy containing it. t

10. A process for preparing alkaline earth metal alloys, which process comprises the step of mixing together in the molten condition cadmium and an alloy with aluminium containing the said alkaline earth metal and then recovering the aluminium.

11. A process for preparing calcium alloys, which process comprises the steps of mixing together in the molten condition metallic cadmium and an aluminium alloy containing calcium and then recovering the aluminium.

GUSTAF NEWTON KIRSEBOM. 

